The Magic Missile is a spell that summons a shimmering projectile that can be launched and controlled by pressing and holding the left mouse button. It also changes color throughout use.
It can be found in Golden Chests inside dungeons or very rarely Underground. The spell costs 10 mana to use and the projectile inflicts 22 damage and will vanish after hitting an enemy or a solid block. It also lights the surroundings much like a torch or the Flamelash spell, but the particles do not drop, therefore are less useful for exploration (besides the open ocean). You can click and hold the Magic Missile over your character, which acts like a light source and a weak shield (if placed right). This item is also extremely useful to harvest cobwebs, vines, pots, etc. By moving the missile over a breakable object, one may obtain the items inside without actually coming into contact with them. It also produces a unique sound upon impact.02:47

Terraria - Magic Missile flamelash

Trivia

This is, perhaps, a reference to Dungeons and Dragons in which magic missile is one of the lowest tier spells a wizard starts with. The spell always hits its target, which is perhaps why you can steer the magic missile into any target.

The Magic Missile displays a particle effect similar to that of the Magic Mirror.

The Magic Missile gives off faint amounts of light and will not be set off if it comes in contact with pots, making it ideal for cave exploration.

Bugs

The Magic Missile caused every player to crash (except if the host uses it, he or she will not crash) on the console versions as of release.Console(Fixed)

Because the cursor can go anywhere on the screen, you can use it to access chests or interact with items from far away, even off the screen.

In the iOS and Android version of Terraria controlling the missile will continue to create more missiles at the expense of using more mana. This makes the missile an effective high-damage weapon. This bug applies the same for the Flamelash.